Control mechanisms of tanning in Corcyra cephalonica

Localisation of a prophenoloxidase in the cytoplasm of plasmatocytes was histochemically demonstrable in Corcyra cephalonica, by incubating the blood with different phenolic substrates. The activation of this latent enzyme was found to be controlled by a protein factor present in the cuticle. The haemolymph prophenoloxidase could be activated in vitro by prior incubation of the blood sample at 0°C. The treatment with NaCl, EDTA, or detergents did not cause any activation. The exposure of blood samples to gamma-rays, repeated freezing and thawing, or addition of the cuticular activator, brought about rapid disruption of the haemocytes causing a release of phenoloxidase and acceleration of melanization of the blood. The administration of α-ecdysone to the last instar larvae induced premature pupation and accentuated the activation of phenoloxidase without altering the level of enzyme activity. The possible regulatory mechanisms of tanning during the development of Corcyra have been discussed.